Skids or beams for furnaces

ABSTRACT

A skid or beam for a slab reheating furnace has a hollow water cooled pipe with a rail welded along the top of the pipe on which the slabs bear. The rail is of inverted channel section with two outer limbs extending downwardly from an upper portion. The lower ends of the outer limbs are welded to the pipe. Preformed grooves extend across the bearing surface of the rail at spaced locations along its length. The channel shaped rail minimizes conduction of heat from the slabs to the pipe and in use the grooves crack and relieve stresses caused by the temperature differences across the rail.

United States Patent Salter et al.

[ 51 Dec. 19, 1972 [54] SKIDS OR BEAMS FOR FURNACES [73] Assignee: TheBritish Iron and Steel Research Association, London, England [22] Filed:Jan. 21,1971

[21] Appl.No.: 108,407

[30] Foreign Application Priority Data March 23, 1970 Great Britain..l3,923/70 [56] References Cited UNITED STATES PATENTS 2,044,165 6/1936Halliwell ..75/l23 K 2,105,838 1/1938 McCormick ..263/6 B 2,553,609 v5/1951 Schmidt ..75/l23 K 2,757,084 7/1956 Cape et al.. 75/123 K3,214,152 10/1965 Molz ..263/6 B 3,236,507 2/1966 McKie 266/5 H3,552,729 l/l97l Hepp et a1 ..263/6 B Primary lixaminer-Gcrald A. DostAttorney-Bacon & Thomas 157] ABSTRACT A skid or beam for a slabreheating furnace has a hollow water cooled pipe with a rail weldedalong the top of the pipe on which the slabs bear. The rail is ofinverted channel section with two outer limbs extending downwardly froman upper portion. The lower ends of the outer limbs are welded to thepipe. Preformed grooves extend across the bearing surface of the rail atspaced locations along its length. The channel shaped rail minimizesconduction of heat from the slabs to the pipe and in use the groovescrack and relieve stresses caused by the temperature differencesacross'the rail.

3,544,094 12/1970 Knaak ..266/5 H 3,304,070 2/1967 Jones ,.266/5 H 11Claims, 6 Drawing Figures 1 I, I, z I I, l L I,

SKlDS OR BEAMS FOR FURNACES In steel making it is known to use furnacesfor reheating stock, such as billets or slabs, with burners both aboveand below the stock and with skids or beams for supporting the stock.The skids or beams include a water cooled pipe and a rail supported onthe pipe which provides a wearing surface and on which the stock bears.In a pusher furnace there are skids for supporting the stock, and thestock is pushed through the furnace and rubs along the rails. In awalking beam furnace there are moving beams and stationary beams and thestock is advanced by being successfully raised off the stationary beamsand deposited again further along the stationary beams by the movingbeams.

The water cooling, which is necessary to maintain the strength of thepipes, causes cooler regions in the stock known as skid marks. One wayof minimizing these skid marks is for the rail to be as hot as possibleand therefore high temperature alloys are necessary. With thesematerials there are difficulties in attaching the rails to the pipe.

Attempts have been made to overcome these attachment problems byinterlocking the rail and pipe without welding them together, but suchsolutions require large rails and are expensive.

An object of this invention is to provide a simple skid or beam in whichthe flow of heat from the stock to the pipe is small.

of the pipe, the rail providing a bearing surface for the stock to beheated, is characterized in that the rail is of inverted channel sectionwith two outer limbs extending downwardly from an upper portion, thelower ends of the outer limbs being welded to the pipe, and in that theupper portion of the rail has a number of stress relievingdiscontinuities spaced along its length.

Previous attempts in which rails of high temperature alloys have beenwelded directly to the pipe have resulted in the rail becoming separatedfrom the pipe. We have realized that the reason, for this is that whenthe skid rail is in use thetop of the rail becomes hot whereas thebottom is maintained at a low temperature because it is welded to thewater cooled pipe. This temperature difference causes the top part'ofthe skid rail to be compressed, and under the stresses set up, plasticdeformation occurs, thereby relieving these stresses. When the furnacetemperature is lowered the rail cools and the top contracts and comesunder tension. This results in the rail tending to curve upwardly at itsends thus applying tensions to the weld so that either the rail, or theweld cracks or both the rail and weld crack. In a pusher furnace thestock is pushed along the rails with a force of hundreds of tons and thestock can catch on a raised portion of the rail that has cracked andbowed and easily tears the rail from the pipe.

The channel section of the rail according to the invention has theresult that less heat is conducted to the, pipe than would have beenconducted by a solid rail of the same dimensions, so that the skid marksare small. The top of the rail is therefore hotter than in aconventional rail with a correspondingly greater tendency to curve butthis problem is reduced by the provision of stress relievingdiscontinuities spaced along the rail.

When the rail according to the invention is in use the upper portionexpands and is thus compressed and under this compressive force plasticdeformation occurs. On cooling the upper portion contracts and comesunder tension which is relieved by the spaced discontinuities. We havefound that a rail according to the invention produces smaller skid marksthan a conventional rail and is not torn off the pipe in use.

After a slab or billet emerges from a reheating furnace it is rolled,and for the rolling to be satisfactory the whole of the slab or billetmust be above a certain temperature. The coolest parts of the slab,namely the skid marks, have to be raised above this certain temperatureand therefore the rest of the slab has to be.

raised to a higher temperature than is necessary for satisfactoryrolling. By diminishing the skid marks by use of skids according to theinvention it is thus possible to lowerthe overall furnace temperaturewhich results in a saving in fuel and an increased life for therefractory materials lining the furnace.

The stress relieving discontinuities can take many forms which arecapable of preventing buildup of stress between opposite ends of theupper portion of the rail. For example the discontinuities could beformed by complete cuts extending laterally through the upper portion ofthe rail at spaced locations along the rail, the cuts being made afterthe rail is cast. The discontinuities could also be formed by laterallyextending rows of holes drilled through the upper portion to formcracking points along which the rail cracks when under tension.Preferably the discontinuities include grooves extending right acrossthebearing .surface of the rail. The walls of the grooves preferablymeet the bearing surface at an obtuse angle to reduce the likelihood ofstock catching on to the edge of the groove. The grooves are preferablyV shaped and can be formed when the rail is cast. When the railcontracts it can crack along one or more of the grooves, and the groovesare so designed that they will crack before either the rail or the weldare otherwise damaged. Preferably the discontinuites extend down atleast part of the outer surfaces of the two outer limbs and terminate inholes passing right through the outer limbs to prevent the cracks fromspreading.

The discontinuities can include grooves extending across the undersideof the upper portion of the rail. Where there are grooves on theunderside of the upper portion as well as on the bearing surface thereis preferably a groove on the underside directly under each groove onthe bearing surface. This promotes cracking.

The rails are preferably made of 50 or 51 percent cobalt steel alloy.The rail is preferably made up of a series of rail lengths weldedtogether.

In a walking beam furnace it is not essential for the rail to becontinuous along the length of the beam although this is preferred. Itis possible to have a series of rail lengths spaced apart from oneanother, but in accordance with the invention'each rail length wouldhave spaced discontinuities.

The pipeis preferably covered with insulating material having twogenerally flat upper surfaces inclined to one another and convergingtowards the rail. This produces less shielding to the slab from burnersbeneath the slab than a circular skid. The pipe can have a generallytriangular cross section. The skid or beam can have more than one pipe.For example three circular pipes can be welded together with their axesparallel, each pipe contacting the othertwo. In this way an effectivelytriangular skid can be fabricated using circular pipes.

In the accompanying drawings:-

FIG. 1 is a cross section of a pusher furnace with skids embodying theinvention,

FIG. 2 is a cross section of one skid embodying the invention,

FIG. 3 is a perspective view of a rail length for the skid of FIG. 2,

FIG. 4 is a side view of another rail length,

' FIG. 5 is a cross section on the line V V of FIG. 4,

and Y FIG. 6 is an end view of the rail of FIG. 4.

' FIG. 1 showsa slab reheating pusher furnace with six skids 1, eachsupported on a supporting structure 2. A slab of steel stock 3 is shownsupported on the skids l. Thereare burners 5 above and below the skids land heat is radiated to the slabs 3 from the burner flames and from thewalls 6 of the furnace.

FIG. 2 shows one of the skids 1 in more detail. The skid 1 includes ahollow skid pipe 9 adapted to allow a cooling fluid to be passedtherethrough, and a rail 10 welded on top of the pipe 9, the railproviding a bearing surface 11 for the stock to be heated. The rail 10is of inverted channel section with two outer limbs 12 extendingdownwardly from an upper portion 13. The

outer limbs 12 are supported on the pipe 9 so'that a space 14 isenclosed by the rail 10 and pipe 9. The lower ends of the outer limbs 12are welded with weld material 15 to the pipe'9. The width of the limbs12 is such that the horizontal cross sectional area of the limbs 12 perunit length of rail is substantially less than the area per unit lengthof the upper surface 11 of the upper portion 13.

The rail 10 is cast from 50 or 51 percent cobalt steel alloy which is awear resisting material which can. be operated for long periods at hightemperature such as 1,000C. The pipe 9 has two generally flat surfaces16 inclined to one another and converging towards the rail 10 over amajor portion of the height of the pipe 9. The maximum height of thepipe exceeds its maximum width. A layer of thermal insulating-material17 surrounds the pipe 9 for insulating the pipe and the insulatingmaterial also has two generally flat surfaces inclined to one another atconverging towards the rail. The insulating material 17 has reinforcingmesh 18 provided within it which is welded at 18 to the pipe to securethe material 17 to the pipe. Refractory filling material 19 is used tofill the gaps between the top of the material 17 and the bottom of therail 10.

The rail 10 is formed of a series of rail lengths each having a numberof stress relieving discontinuities 20 spaced along its length as can beseen in FIG. 3. The rail length is 0.45 meters long and thediscontinuities 20 are spaced at about 5 centimeter intervals.

The discontinuities 20 are formed when the rail lengths are cast andconsist of V shaped grooves extending right across the bearing surface11 of the rail and down at least part of the outer surfaces 21 of thetwo outer limbs 12. The grooves 20 terminate in holes the grooves are V"shaped the walls of the grooves meet the bearing surface 1 1 at anobtuse angle.

Each end of each rail length is chamfered at 23 along its upper portionso that when two rail lengths are welded together a stress relievingdiscontinuity is formed between the two adjacent rail lengths.

Similarly each end of each rail length is formed with semi-circularrecesses 25 in the outer limbs 12 so that when two adjacent rail lengthsare welded together the recesses 25 on adjacent limbs together formholes passing right through the outer limbs 12 similar to the holes 22.v

The bottom end of each limb 12 is chamfered at 26 to allow it to bewelded to the pipe 9 with weld material 15 as can be seen in FIG. 2. Theends of each raillength are provided with welding chamfers 27 on theportion of the limbs 12 below the recesses 25 to allow adjacent raillengths to be welded together.

I The rail 31 length shown in FIGS. 4 to 6 differs from that in FIG. 3in three respects. The first difference is that in addition to thegrooves 20 there are grooves 30 extending across the underside of theupper portion 13 of the rail. The grooves 30 are directly under thegrooves 20. The second difference is that the holes 22 are nearer thebottom of the outer limbs 12. The third difference is that the ends32'of the rail length 31 do not coincide with one of thediscontinuities. Instead the ends 32' are such that when two raillengths 31 are welded together the weld is mid way between two grooves20. Each end 32 has a face 34 at right angles to the length of the rail31 and two inclined faces 36 and 38. To connect two rail lengths theface 32 of one length is butted against the similar face of the nextadjacent rail lengths and the groove formed by the faces 36 and 38 iscompletely filled with weld metal.

After use of the'skid according to the invention it is found thattherail has cracked along at least some of the grooves .20. These cracksare contained and cause no disadvantage. The V shaped grooves 20 ensurethat there is no tendency for stock to catch on to a portion of rail 10and hence tear the rail 10 off the pipe 9. The rail is also found toreduce the skid marks in comparison with known rails.

- We claim:-

1. A skid'or beam for a furnace includinga hollow.

pipe adapted to allow a cooling fluid to be passed therethrough and arail welded on top of the pipe, the rail providing a bearing surface forthe stock to be heated, in which the improvement comprises a rail ofinverted channel section with two outer limbs extending downwardly froman upper portion, the lower ends of the outer limbs being continuousthroughout the length of the rail and being welded to the pipe, and theupper portion of the rail having a number of stress relievingdiscontinuities spaced along its length.

2. A skid or beam as claimed in claim 1 in which the discontinuitiesinclude grooves extending right across the bearing surface of the rail.

3. A skid or beam as claimed in claim 2 in which the walls of thegrooves meet the bearing surface at an obtuse angle.

4. A skid or beam as claimed in claim 1 in which the discontinuitiesinclude grooves extending across the underside of the upper portion ofthe rail.

5. A skid or beam as claimed in claim 2 in which the discontinuitiesfurther include a groove extending across the underside of the upperportion directly under each groove on the bearing surface.

6. A skid or beam as claimed in claim 1 in which the discontinuitiesextend down at least part of the outer surfaces of the two outer limbsandterminate in holes passing right through the outer limbs.

7. A skid or beam as claimed in claim 1 in which the rail is made of 50or 51 percent cobalt steel alloy.

8. A skid or beam as claimed in claim 1 including a layer of thermalinsulating material for insulating the pipe.

9. A skid or beam as claimed in claim 1 in which the rail is made up ofa series of rail lengths welded together.

10. A skid or beam as claimed in claim 1 in combination with a furnacewhich has heating means disposed both below and above the skid or beam.

11. A skid or beam as claimed in claim 1 wherein said stress relievingdiscontinuities are provided in the bearing surface of the rail.

l060ll 0216

1. A skid or beam for a furnace including a hollow pipe adapted to allowa cooling fluid to be passed therethrough and a rail welded on top ofthe pipe, the rail providing a bearing surface for the stock to beheated, in which the improvement comprises a rail of inverted channelsection with two outer limbs extending downwardly from an upper portion,the lower ends of the outer limbs being continuous throughout the lengthof the rail and being welded to the pipe, and the upper portion of therail having a number of stress relieving discontinuities spaced alongits length.
 2. A skid or beam as claimed in claim 1 in which thediscontinuities include grooves extending right across the bearingsurface of the rail.
 3. A skid or beam as claimed in claim 2 in whichthe walls of the grooves meet the bearing surface at an obtuse angle. 4.A skid or beam as claimed in claim 1 in which the discontinuitiesinclude grooves extending across the underside of the upper portion ofthe rail.
 5. A skid or beam as claimed in claim 2 in which thediscontinuities further include a groove extending across the undersideof the upper portion directly under each groove on the bearing surface.6. A skid or beam as claimed in claim 1 in which the discontinuitiesextend down at least part of the outer surfaces of the two outer limbsand terminate in holes passing right through the outer limbs.
 7. A skidor beam as claimed in claim 1 in which the rail is made of 50 or 51percent cobalt steel alloy.
 8. A skid or beam as claimed in claim 1including a layer of thermal insulating material for insulating thepipe.
 9. A skid or beam as claimed in claim 1 in which the rail is madeup of a series of rail lengths welded together.
 10. A skid or beam asclaimed in claim 1 in combination with a furnace which has heating meansdisposed both below and above the skid or beam.
 11. A skid or beam asclaimed in claim 1 wherein said stress relieving discontinuities areprovided in the bearing surface of the rail.